Mobile phones, personal digital assistants (“PDAs”), digital cameras, MP3 players, and other portable electronic devices utilize solid state lighting (“SSL”) devices (e.g., LEDs) for backlighting. SSL devices are also used for signage, indoor lighting, outdoor lighting, and other types of general illumination. FIG. 1A is a cross-sectional view of a conventional SSL device 10a with lateral contacts. As shown in FIG. 1A, the SSL device 10a includes a substrate 20 carrying an LED structure 11 having an active region 14, e.g., containing gallium nitride/indium gallium nitride (GaN/InGaN) multiple quantum wells (“MQWs”), positioned between N-type GaN 15 and P-type GaN 16. The SSL device 10a also includes a first contact 17 on the P-type GaN 16 and a second contact 19 on the N-type GaN 15. The first contact 17 typically includes a transparent and conductive material (e.g., indium tin oxide (“ITO”)) to allow light to escape from the LED structure 11. In operation, electrical power is provided to the SSL device 10a via the contacts 17, 19, causing the active region 14 to emit light.
FIG. 1B is a cross-sectional view of another conventional LED device 10b in which the first and second contacts 17 and 19 are opposite each other, e.g., in a vertical rather than lateral configuration. During formation of the LED device 10b, a substrate 20, similar to the substrate 20 shown in FIG. 1A, initially carries an N-type GaN 15, an active region 14 and a P-type GaN 16. The first contact 17 is disposed on the P-type GaN 16, and a carrier 21 is attached to the first contact 17. The substrate 20 is removed, allowing the second contact 19 to be disposed on the N-type GaN 15. The structure is then inverted to produce the orientation shown in FIG. 1B. In the LED device 10b, the first contact 17 typically includes a reflective and conductive material (e.g., silver or aluminum) to direct light toward the N-type GaN 15.
One drawback with existing LEDs is that they do not emit white light. Instead, LEDs typically emit light within only a narrow wavelength range. For human eyes to perceive the color white, a broad range of wavelengths is needed. Accordingly, one conventional technique for emulating white light with LEDs is to deposit a converter material (e.g., a phosphor) on an LED die. FIG. 1C shows a conventional SSL device 10c that includes a support 2 carrying an LED die 4 and a converter material 6. In operation, an electrical voltage is applied to the die 4 via contacts having an arrangement generally similar to that shown in either FIG. 1A or FIG. 1B. In response to the applied voltage, the active region of the LED die 4 produces a first emission (e.g., a blue light) that stimulates the converter material 6 to emit a second emission (e.g., a yellow light). The combination of the first and second emissions appears white to human eyes if matched appropriately. As discussed in more detail below, using phosphor converter materials to “convert” blue light into white light has certain drawbacks. Accordingly, there is a need for light emitting devices that can produce light at a particular wavelength without phosphor converter materials.